Flow Visualization Study of Wake-Stabilized Diffusion Flames in a Crossflow: Effects of Crossflow Turbulence
Abstract
Effects of crosswind turbulence on the mechanisms and flow structures affecting emissions from non-premixed wake stabilized flames from elevated stacks are investigated. In the current work, two conditions of upstream crossflow are tested to investigate the effects of turbulence on the flame, including the turbulent flow with enhanced freestream turbulence that is generated by a passive grid placed upstream of the burner, and smooth flow with ambient turbulence for baseline comparisons. The experimental method of Mie scattering flow visualization is used to investigate the effects of turbulence. The addition of freestream turbulence has been found to make changes to the flame characteristics and the development of vortical structures in the separated shear layer, which are closely associated with increases in combustion inefficiency. The fuel stripping mechanism was proposed to be responsible for inefficient combustion; a few bits of unburnt fuels are observed to be drawn through adjacent flame pockets, and finally are ejected away from the underside of flame without combustion. The Mie scattering images combined with combustion inefficiency data indicated the bypass-transition in the shear layer plays an important role in the fuel stripping mechanism.